Polymers for use in optical devices

ABSTRACT

Optical devices fabricated from solvent processible polymers suffer from susceptibility to solvents and morphological changes. A semiconductive polymer capable of luminescence in an optical device is provided. The polymer comprises a luminescent film-forming solvent processible polymer which contains cross-linking so as to increase its molar mass and to resist solvent dissolution, the cross-linking being such that the polymer retains semiconductive and luminescent properties.

FIELD OF THE INVENTION

[0001] The invention relates to polymers for use in optical devices suchas photoluminescent and electroluminescent devices.

BACKGROUND TO THE INVENTION

[0002] Polymer LEDs were first described by Burroughes et al (PCTG390/00584). Devices based on copolymers (Holmes et al, PCT GB91/01420;PCT GB91/01421) multilayers (PCT GB93/01573; PCT GE93/01574) and withhigh electron affinity polymers have also been reported (PCTGB94/01118).

[0003] Conjugated poly(3-alkylthienylene)s have been prepared, andrevewed by J. Roncali (Chem Rev, 1992, 92, 711) and applications inelectroluminescent devices were reported by Y. Ohmori et al. (Jpn. J.Appl. Phys. Part 2, 1991, 20 (11B), L1938-1940. Reaioregularpoly(3-alkylthienylene)s have been described by R. D. McCullough, R. D.Lowe, M. Jayaraman, and D. L. Anderson, (J. Org. Chem., 1993, 58, 904).Solvent dependent chircotical behaviour has been reported forregioregular poly(3-alkylthienylene)s M. M. Bouman, E. E. Havinga, R. A.J. Janssen and E. W. Meijer, Mol. Czyst. Liq. Crist., 1994, 256, 439).Regiorandom hydroxy-functionalised polythiophene copolymers have beenreported (C. Della Casa, E. Salatelli, F. Andreani and P. CostaBizzarri, Makromol. Chem. Makromol. Symp., 1992, 59, 233), and thepotential for cross linking was noted (J. Lowe and S. Holdcroft, Polym.Prepr., 1994, 35, 297-298).

[0004] More advanced polymeric LEDs can involve the use of both emissiveand charge transport materials in order to improve the efficiency of thedevice [P. L. Burn, A. B. Holmes, A. Kraft, A. R. Brown, D. D. C.Bradley, R. H. Friend, Mat. Res. Soc. Symp. Proc., 1992, 247, 647; A. R.Brown, D. D. C. Bradley, J. H. Burroughes, R. H. Friend, N. C. Greenham,P. L. Burn, A. B. Holmes and A. Kraft, Appl. Phys. Lett., 1992, 61,2793; T. Nakano, S. Dci, T. Noguchi, T. Ohnishi Y.-Iyechika, SumitomoChemical Company Limited, U.S. Pat. No. 5,317,169, May 31, 1994].

[0005] Emissive polymers are the main active layer in polymer LEDs.Singlet excitons are formed under double charge injection which thendecay radiatively to produce light emission. On the other hand, chargetransport polymers have also been found to play an important role inenhancing the internal quantum efficiency of devices (photons emittedper electron injected), decreasing working voltages and in increasingthe life-time of the devices. This was first shown by use of the knowncharge transporting molecule (PBD)[2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole] as a blend inpoly(methyl methacrylate) as mentioned above [Burn et al.; Nakano etal.]. Recently, high efficiency (4a) blue electroluminescence has beenachieved by means of charge-transporting layers using polyvinylcarbazole(PVK) as a hole-transporting material and PBD-blended with poly(methylmethacrylate) (PMMA) as an electron transporting material in themulti-layer device [ITO/PVK/PQ(polyquinoline)/PBD+PMMA/Ca] [I. D.Parker, Q. Pei, M. Marrocco, Appl. Phys. Lett., 1994, 65 (10), 1272].The role of the charge transport layer in LEDs include: (i) assistingeffective carrier injection from the electrode to the emitting layer(ii) confining the carriers within the emitting layer and thusincreasing the probability of recombination processes through radiativedecay, leading to light emission (iii) preventing the quenching ofexcitons at the boundary between an emitting material and the electrode.

[0006] Most common conjugated polymers are more easily p-doped and thusexhibit hole-transport properties. On the other hand, electron transportand electron injection in polymer LEDs have proved to be more difficultand are thus required in order to improve device efficiency andperformance.

[0007] An aromatic oxadiazole compound such as PBD is well known to be auseful electron transport material [K. Naito, Jpn. Kokai Tokkyo Koho, JP05,202,011,1993; S. Lunak, M. Nepras, A. Kurfurst and J. Kuthan, Chem.Phys., 1993, 170, 67]. Multi-layered LED devices with improvedefficiency have been reported using evaporated PBD or a spin-coatedPBD/PMMA blend as an electron transport layer.

[0008] In each case, however, problems that will lead to devicebreakdown (such as the aggregation and re-crystallisation of PBD) may beexpected to occur under the influence of an electrical field ortemperature increase when the device is working [C. Adachi, et al, Jpn.J. Appl. Phys., 1988, 27, L269; C. Adachi, S. Tokito, T. Tsutsui, S.Saito, Jpn. J. Appl. Phys. 1988, 27, L713; Y. Hamada, C. Adachi, T.Tsutsui, S. Saito, Jpn. J. Appl. Phys. 1992, 31, 1812; K. Naito, A.Miura, J. Phys. Chem., 1993, 97, 6240].

[0009] Conjugated polymers that contain aromatic and/or heteroaromaticrings have enjoyed considerable interest because of their potentialelectrical conductivity after being doped and electroluminescentproperties. However, there is a severe processibility problem forconjugated polymers as they are usually insoluble or infusible becauseof the rigidity of the main polymer chain and strong intermolecularforcesbetween polymer chains. One way to improve the processibility ofthese polymers is to prepare a soluble precursor which can then beconverted into a rigid conjugated polymer, as can be done withpoly(p-phenylenevinylene) (PPV) (A) [A green yellow emitter, prepared bythe sulfonium precursor route: P. L. Burn, D. D. C. Bradley, R. H.Friend, D. A. Halliday, A. B. Holmes, R. W. Jackson and A. Kraft, J.Chem. Soc., Perkin Trans., 1992, 1, 3225]. Another way is to generate afully conjugated material while increasing solubility by attaching bulkyand flexible alkyl or alkoxy groups onto the main chain therebyweakening the intermolecular forces (as shown in the case of alkyl- oralkoxy-substituted PPV in (B) and (C)). A third way is to attach orinsert a photoluminescent chromophore to a flexible polymer chain sincethe flexible chain segments will enhance the solubility in conventionalorganic solvents. This has been shown in the case of a block copolymerconsisting of π-conjugated active blocks sandwiched between non-activeflexible blocks (R. Gill, G. Hadziioannou, J. Herrema, G. Malliaris, R.Wieringa, J. Wildeman, WPI Acc. No.94-234969; Z. Yang, I. Sokolik, F. E.Karasz, Macromolecules, 1993, 26 (5), 1188; Sumitomo Chem. Co. Ltd., JP5320635).

[0010] In order to improve the performance of polymer LEDs, theluminescent polymer needs to be used in association with a chargetransport polymer. Conventionally, charge transport materials may beused as single layers between the emitting layer and the electrodes.Alternatively, blends may be used.

[0011] Thus, prior art polymers used in optical devices suffer fromsusceptibility to solvents and morphological changes owing to low glasstransition temperatures. Moreover, when molecular electron transportmaterials are used in such optical devices, problems involving theaggregation and recrystallisation of the material may lead to devicebreakdown.

SUMMARY OF THE INVENTION

[0012] In one aspect, the present invention provides a semiconductivepolymer capable of luminescence in an optical device, such as aphotoluminescent or electroluminescent device. The polymer comprises aluminescent film-forming solvent processible polymer which containscross-linking so as to increase its molar mass and to resist solventdissolution, the cross-linking being such that the polymer retainssemiconductive and luminescent properties.

[0013] By increasing the molar mass of the polymer the deleteriouseffects of susceptibility to solvents and morphological change owing tolow glass transition temperatures are avoided. Surprisingly, thecross-linked polymers retain their semiconductive and luminescenceproperties. Luminescent and electroactive polymer thin films such asthose used in optical devices may therefore be stabilised. Because thethin films resist dissolution in common solvents this enables depositionof further layers of, for example, electroactive polymer films bysolvent coating techniques thereby facilitating device manufacture. Thecross-linked semiconductive polymers retain all their desirableluminescence properties and have the advantage of exhibiting enhancedmorphological stability under device operation.

[0014] The cross-linking may be formed in the semiconductive polymer bythermal cross-linking, chemical cross-linking or photochemicalcross-linking. Cross-linking methodology for polymers is well-known. Forexample, the cross-linking of polymers for photoresists bythermal,chemical and photochemical methods has been reviewed; (S. Paul, CrossLinking Chemistry of Surface Coatings, in Comprehensive Polymer Science,G. Allen (Ed.), Pergamon, Oxford, 1989, Vol. 6, Ch.6, pp. 149-192; S. R.Turner and R. C. Daly, Photochemical and Radiation-sensitive Resists, inComprehensive Polymer Science, G. Allen (Ed.), Pergamon, Oxford, 1989,Vol. 6, Ch.7, pp. 193-225; S. P. Pappas, Photocrosslinking inComprehensive Polymer Science, G. Allen (Ed.), Pergamon, Oxford, 1989,Vol. 6, Ch.5, pp. 135-148). In addition, an example of cross linking ofpolymers through ring opening metathesis polymerization ofcyclooctene-5-methacrylate was reported by B. R. Maughon and R H Grubbs,(Polym. Prepr., 1995, 36, 471-472).

[0015] A particularly useful example of thermal cross-linking involvesthe use of azide groups usually attached to the polymer main chain by aspacer group. At a temperature typically in the range of 80° C. to 250°C. the aliphatic azide will either form a pyrazoline adduct with adouble bond or decompose to form a highly reactive nitrene which canthen form cross-links with other polymers. An aryl azide will behavesimnilarly in the range 20° C. to 250° C. The spacer is advantageouslynon-rigid. Preferably the spacer comprises —(CH₂)_(n) or —(CH₂)_(n)—Ar—in which n is an integer preferably in the range 2 to 20 and Ar is anaryl group, preferably a phenylene group. A good example of such aspacer is a —(CH₂)₁₁— group.

[0016] Chemical cross-linking may be effected using diisocyanates oractivated dicarboxylic acid derivatives to react with terminalfunctional groups (e.g. —OH) on the soluble polymer. In this wayurethane or ester linkages can be created. Alternatively, a lowmolecular weight bifunctional or polyfunctional compound (e.g. an epoxyresin) can be blended with the solvent processible polymer for thepurpose of reacting chemically with existing functional groups (e.g.amino etc) in the polymer main chain or on the side chains of thepolymer. Suitable cross-linking agents include formaldehyde or otheraldehydes, bis or polyfunctional azides such as 1,6-bisazidohexane, andDolyisocyanates.

[0017] Photochemical cross-linking may be effected by any side chainsubstituent capable of becoming activated upon irradiation with light ofappropriate energy, usually UV light. For example, cinnamate esters willundergo [2+2]-cycloaddition under appropriate conditions, typicallyirradiation of the polymer film at ambient temperature with a mediumpressure Hg lamp. Also, photolysis of alkyl or aryl azides over a widetemperature range, preferably −50° C. to +50° C., can generate reactivenitrene intermediates which can cross-link the polymer.

[0018] The luminescent film-forming polymer and the cross-linked formthereof according to the present invention may be luminescent either byvirtue of a luminescent main chain or a luminescent side chain. Thepolymer may comprise any such film-forming polymer, including copolymersand ollgomers. The luminescent main chain polymers have been describedin PCT GB 90/00584 and PCT GB91/01420, for example. Such polymersinclude poly(arylene vinylene) derivatives. Particularly usefulpoly(arylenevinylene) polymers in the present invention include polymersof general formula B and which carry cross-linkable functionality as anattachment. Electroluminescent polyarylenes are also particularly usefulin the present invention, including polyheteoarylenes, especially thepolythiophenes. Polythiophene copolymers are known to be capable ofluminescence and substituted poly(3-alkyl thienylenes) are preferred.

[0019] Statistical copolymers of substituted poly(3-alkylthienylene)scontaining regioregular head to tail linkages can be made according toK. A. Murray, S. C. Moratti, D. R. Baigent, N. C. Greenham, K. Pichler,A. B. Holmes and R. H. Friend, in Synth. Met., 1995, 69, 395-396 andthen cross-linked. The side chain alkyl substituents or a fractionthereof carry functionality which can be employed in chemical,photochemical or thermal cross-linking processes.

[0020] Further examples of polymers having a luminescent main chain arethose which have the electroluminescent segments in scheme 2 belowforming part of the polymer main chain. In a preferred embodiment of theinvention, the polythiophene copolymer is of the general formula

[0021] in which R′ is a solubilising group, R″ is a spacer groupcross-linking the main chain to another polymer, and x, y and n are eachintegers, wherein x:y is in the range 19:1 to 1:2 and n is in the range3 to 100.

[0022] Preferably, R′ is —C₆H₁₃.

[0023] Where the polymer includes a luminescent side chain, this sidechain may incorporate any luminophoric group such as a speciescontaining. at least 3 unsaturated units in conjugation. Preferably theluminescent side chain comprises a distyryl benzene. Where the polymerincludes a luminescent side chain, there is no need for the main chainof the polymer itself to be luminescent but the polymer should betransparent to the emitted light. Various polymers may therefore be usedto form the main chain. Especially useful polymers include polystyrenes,polyacrylates, polysiloxanes, and polymethacrylates which are preferred.Polymethacrylates are discussed in further detail below.

[0024] In one embodiment of the invention, the polymer further comprisesa charge transport segment which is present in the polymer main chain orcovalentlv linked thereto in a charge transport side chain.

[0025] In a further aspect of the invention a polymer is provided whichis capable of charge transport, preferably electron transport, in anoptical device such as an electroluminescent device. The polymercomprises a film-forming polymer which is solvent processible or formedfrom a processible precursor polymer and which includes a chargetransport segment in the polymer main chain or covalently linked theretoin a charge transport side chain.

[0026] The polymers may be used as both charge transporting and/orelectroluminescent materials in polymer light emitting devices. Thepolymers may therefore include charge transport functional segments andelectroluminescent functional segments either as a side chain group orin the main chain of the polymer. Precursor polymers leading, after aconversion step, to intractable final polymers may be used, as well asfully processible polymers. Each type of polymer can have specificadvantages in processing multi-layered structures.

[0027] The charge transport segment may comprise the moiety Ar₁-Het-Ar₂in which Ar₁ and Ar₂ are the same or different From one another and arearomatic units. Examples of these aromatic units are set out below inScheme 1. Het is a heteroaromatic ring, the electronic structure ofwhich favours charge transport. Examples include oxidiazole,thiadiazole, pyridine, pyrimidine and their benzo-fused analogues suchas cuinoline. Heteroaromatic rings which are electron deficient andtherefore enhance charge injection and transport are generally useful.

[0028] Ar₁, Ar₂ are aromatic, heteroaromatic, fused aromatic derivativesthereof, or double bonds:

[0029] The electroluminescent segments may comprise conjugatedphotoluminescent chromophore segments as illustrated in Scheme 2.

[0030] The side chair (co)polymer consists of any backbone polymercontaining side chain modifications with luminescent and/or electrontransporting segments. A typical example is a poly(methacrylate) thatcontains charge transport segments and/or luminescent segments in thependant side group as shown in Scheme 3.

[0031] The side chain polymer may contain an optional third functionalsegment that will play a cross-linking role so as to improve thestability of the poly(methacrylate) i.e. by raising the glass transitiontemperature (T_(g)) The third segment may be a chemically cross-linkablegroup such as an epoxide, a thermally cross-linkable group such as anazide, or a photocross-linkable group such as a cinamate or a stilbenegroup.

[0032] Scheme 3 Illustration of a side chain copolymer (usingpoly(methacrylate) as an example)

[0033] The main chain polymers and copolymers referred to herein are(co)polymers that contain transport segments and/or electroluminescentsegments along the polymer or copolymer backbone with or withoutflexible spacers as illustrated by a representative example in Scheme 4.

[0034] The polymers described in the present invention are particularlysuitable for use as electron transport layers in a multilayer LED deviceeither as a blend with another electroluminescent polymer or as one ofthe components in a copolymer with another electroluminescent segment.This improves both the internal quantum efficiency and deviceperformance.

[0035] Preparation and Application of Side Chain Polymers

[0036] Poly(methacrylates) have many advantages such as hightransparency, high resistance to chemicals, and good mechanicalstrength. It is also relatively easy to synthesise high molecular weightpolymers as well as multi-functional copolymers.

[0037] To illustrate this general concept, a range of aromaticoxadiazole bonded polymers (especially poly(methacrylates)) have beensynthesised and investigated incorporating monomers as shown in Scheme5. These (co)polymers can be used in association with emissive polymersin different ways (single layer, blended layer and copolymer layer) togive devices with improved performance.

[0038] In a previous patent application (PCT/GB93/02856) a range ofpoly(methacrylate) derivatives containing chromophores D featuring blueemission were synthesised. The chromophoric groups F, G, H, I comprisedtwo or three conjugated aryl rings (distyrylbenzene units) attached tothe poly(methacrylate) chain via covalent linkages. This is arepresentative example of the numerous possibilities for blue size chainmodified light emitting polymers. Crosslinking and copolymerisation withpolymers carrying charge transporting segments make these materialsparticularly attractive candidates for blue light emission.

[0039] The polymer capable of charge transport is generally used in anoptical device as a functional polymer layer between anelectroluminescent polymer layer and a charge injection electrode. Thislayer plays a role in enhancing charge and especially electronicinjection from the metal electrode (usually a cathode) and chargetransport. The polymer may balance the charge injection in a multi-layerpolymer LED with improvement of device performance.

[0040] In a further aspect, the present invention provides use of apolymer as described above in an optical device, preferably anelectroluminescent device. The present invention also provides anoptical device which comprises a substrate and a polymer as definedabove supported on the substrate. The optical device is preferably anelectroluminescent device. Typically, the polymer is used in suchdevices as a thin film. In operation the cross-linked semiconductivepolymers retain desirable luminescent properties and have the advantageof exhibiting enhanced morphological stability.

[0041] The present invention will now be described in further detail, byway of example only, with reference to the accompanying drawings inwhich:

[0042]FIG. 1 shows a graph of internal quantum efficiency againstcurrent for the devices ITO/PPV/PMA-PPD/Ca and ITO/PPV/Ca;

[0043]FIG. 2 shows a graph of current against field for the devices ofFIG. 1;

[0044]FIG. 3 shows a graph of luminance L against voltage V for thedevice ITO/PPV/PMA-TPV+PMA-PPD/Ca;

[0045]FIG. 4 shows a graph of efficiency against current for the deviceof FIG. 3;

[0046]FIG. 5 shows a graph of luminance against wavelength lambda forthe device ITO/PPV/PMA-TPV+PMk-PED/Ca;

[0047]FIG. 6 shows a graph of current against voltage for the deviceITO/PPV/PMA-TPV-PBD/Al;

[0048]FIG. 7 shows a graph of luminance against wavelength lambda forvarious LED devices ITO/PPV/Ca, ITO/PPV/Copolymer of 16 and 9b (1:1)/Alindicating cross-linking of the distyrlbenzene chromophore as a functionof time;

[0049]FIG. 8 shows a graph of efficiency against current for the deviceITO/PPV/copolymer/Al of FIG. 7;

[0050]FIG. 9 shows a graph of luminance against wavelength lambda forthe copolymer device of FIG. 7;

[0051]FIG. 10 illustrates representative polythiophenes forcross-linking;

[0052]FIG. 11 shows cross-linking of a 9:1 copolymer 45b before andafter heating;

[0053]FIG. 12 shows a graph of a TV-VIS absorption spectrum. ofcopolymer 49;

[0054]FIG. 13 shows a photoluminescence spectrum of polymethacrylate 49(p=05, q=0.3, r=0.2) with three functional groups;

[0055]FIG. 14 shows a UV-VIS absorption spectrum of the 3-unitecopolymer of FIG. 13 upon exposure to UV light as a function of time;

[0056]FIG. 15 shows an electroluminescent spectrum of a light emittingdevice using polymer 49 as an emissive layer (ITO/polymer 49/Ca, withinternal quantum efficiency of 0.1%)

[0057]FIG. 16 shows graphs of current and luminance against voltage fora cross-linked polythiophene (45b, 9:1) device; and

[0058]FIG. 17 shows an electroluminescent spectrum of a cross-linkedthiophene device of FIG. 16.

EXAMPLE 1

[0059] The Synthesis of Methacrylate-PPD Monomer (9a)—Scheme 5

[0060] Preparation of aldehyde (2): Sodium borohydride (4.9 g, 0.13 mol)pellets were added to a solution of terephthaldehyde mono-(diethylacetal) (39.9 g, 0.19 mol) in MeOH (150 ml) at 0° C. (using an icebath). The reaction mixture was stirred for 1.5 h at 0° C. Water (100ml) and HCl (10M, 200 ml) were added and the mixture stirred at roomtemperature for 1.5 h. After removing MeOH under reduced presure, ethylacetate (200 ml) was added. The organic layer was washed with sodiumhydrogen carbonate solution and water. The clear organic layer was driedwith anhydrous sodium sulfate. The crude product (20.35 g) wasrecrystallized from chloroform/hexane and was obtained as fine crystals(18.79 g 73%); m.p.43-45° C.

[0061] Preparation of 4-(acetyloxy-methyl)benzoic acid (3) Triethylamine(15.4 ml, 110.4 mmol) was added to a solution of aldehyde (2) (12.57 g,92.4 mmol) in THF (50 ml) and cooled to 0° C. Acetyl chloride (7.91 g,110.4 mmol) was then gradually added over 25 minutes, and the mixturewas then left to stir for two hours at room temperature. After one hour,ethyl acetate (200 ml) was added and the solution washed with sodiumcarbonate (100 ml), HCl (17 a., 50 ml) and water (100 ml) respectively.The organic layer was then dried over sodium sulfate and the solventremoved under reduced pressure to give an oil which crystallised whencooled. Re-crystallisation in methanol-hexane gave light yellowcrystals.

[0062] 4-[acetyloxy-methyl]benzaldehyde: (15.39 g, 94%). m.p. 33-35° C.;R_(f) 0.62 (ether). ν_(max) (KBr)/cm⁻¹: 1735 S (O—C═O), 1686 s (H—C═O)1608 m (phenyl absorption), 1384, 1369, 1253, 1212, and 811; λ_(H) (250MHz, CDCl₃) 2.10 (3H, s, CH₃), 5.14 (2H, s, CH₂O—), 7.41 (2H, d, J 8.1,Ar—H), 7.89 (2H, d, J 8.1, Ar—H) and 9.98 (1H, s, CHO). δ_(C) (63.5 MHz;CDCl₃) 20.8 (CH₃), 65.4 (CH₂) 128.2, 129.9, 142.7, 141.8 (phenylcarbons), 170.6 (O—C═O) and 191.8 (H—C═O).

[0063] 4-[acetyloxy-methyl]benzaldehyde (15.3 g, 86.5 mmol) in acetone(250 ml) was then reacted with Jones reagent (33.0 ml, a three-foldexcess) while stirring (exothermal reaction). This was stirred for 2 hbefore filtering out the green solid. The green solid was then driedunder reduced presure and dissolved in ethyl acetate (400 ml) and washedwith sodium carbonate solution and water until neutral. After removal ofsolvent, a crop of yellow crystals (13.3 g) was obtained which was thenrecrystallised in chloroform-hexane to give a white crystal (3) (12.62g, 76%). m.p.120-123° C.; R_(f) 0.29 (1:1 Hexane-ether v/v).

[0064] Preparation of 4-tert-butyl benzoic hydrazide (5a): Hydrazinehydrate (9.4 ml, 194 mmol). was added to methyl 4-tert-butyl benzoate(25.3 g, 29 mmol) in ethanol (25 ml) and then refluxed under nitrogenfor 18 h. The solvent was then removed under reduced pressure and thesolid residue recrystallised from hot toluene-hexane (140 ml, 10:4toluene-hexane v/v), to give colourless crystals of 4-tert-butyl benzoichydrazide (19.25 g, 760%). m.p.126-128° C.

[0065] Preparation of 1-(D-tert-butylbenzoyl)-2-(4-acetyloxy-methyl-benzoyl)-hydrazine (6): Thionyl chloride(30 ml) was added to (3) (15.10 g, 77.8 mmol) in a 250 ml three-neck RBflask and refluxed for 40 minutes at 70-80° C. After removing the excessthinoyl chloride under vacuum, the brown oil (4) was then washed withchloroform (3×15 ml). The residue was then dissolved in dry pyridine(120 ml). Hydrazide (5a) (14.9 g, 77.8 mmol) was at last added. Thebrown solution was stirred and refluxed for 3 h before pouring themixture into ice water (700 ml) to precipitate the product which wasthen washed with water and dried at 80° C. in vacuo to give the product.The product can be further purified by recrystallisation in toluene togive white crystals. m.p.229-230° C. (with liquid crystal behaviour andeasy decomposition in air); δ_(H) (250 MHz, CDCl₃) 1.32 (9H, s, ^(t)Bu),2.13 (3H, s, CH₃CO), 5.13 (2H, s, CH₂), 7.41 (4H, t) and 7.81 (4H, m,Ar—H), 9.59 and 9.72 (2H, d, —NHNH—); δ_(C) (63.5 MHz, CDCl₃) 20.9(CH₃), 31.1 (C(CH₃)₃), 65.4 (CH₂), 125.7, 127.1, 127.6, 128.0, 128.3,130.4, 131.1, 140.5 (C), 156.1 (C═O), 163.9 (C═O); ν_(max) (CHCl₃)/cm⁻¹:3233 (N—H), 1736 (O—CO), 1672 (NH—CO), 1633, 1445, 1450 (phenylabsorption); [Found: C, 68.66; H, 6.64; N, 7.65. C₂₁H₂₄N₂O₄ requires C,68.48; H, 6.52; N, 7.61%].

[0066] Preparation of2-(para-tert-butyl-phenyl)-5-(4-acetyloxy-methyl-phenyl)-1,3,4-oxadiazole(7a): POCl₃ (35 ml) was added to (6a) (3.31 g, 8.99 mmol) and refluxedfor 18 h under nitrogen. POCl₃ was distilled from the reaction mixturebefore pouring the residue into ice water. Extraction with ethyl acetate(2×200 ml) gave a yellow oil after removal of solvent. The crude product(TLC showed 3 spots) was purified by flash column chromatography usinghexane-ether (10:1 to 3:7 v/v) yielding colourless crystals (7a) (1.02g, 220c). m.p. 93-950C; R_(f) 0.24 (1:1 hexane-ether v/v) δ_(H) (250MHz, CDCl₃) 1.36 (9H, s, ^(t)Bu), 2.14 (3H, s, CH₃CO), 5.18 (2H, s,CH₂), 7.54 and 8.07 (4H, m, Ar—H); σ_(C) (63.5 MHz, CDCl₃) 21.0 (CH₃CO),31.1 (C (CH₃) 3), 35.1 (C (CH₃)₃), 66.5 (CH₂), 121.1 and 126.1, 126.8,139.7 (Ar—CH₂OAc), 123.9, 127.1, 128.6, 155.5 (Ar—^(t)Bu), 164.1 (C) and164.8 (C) and 170.7 (C═O); [found: C, 72.12; H, 6.29; N, 8.10. C₂₁H₂₂O₃Nrequires C, 72.0; N, 8.0; H, 6.3%]; m/z (EI) 350 (80), 335 (100%), 161(30) and 43 (30) [Found: (M⁺) 350.1630. C₂₁H₂₂O₃N requires M, 350.1630].

[0067] Preparation of2-(para-tert-butyl-phenyl)-5-(4-hydroxyl-methyl-phenyl)-1,3,4-oxadiazole(8a): Oxadiazole (7a) (0.67 g, 1.91 mmol) was added to a solution ofsodium hydroxide (0.11 g, 2.75 mmol) in ethanol (30 ml), and the mixturestirred for 2 h. The mixture was poured into aqueous sodium bicarbonate(5%, 100 ml) and a white precipitate which formed, was collected byfiltration. The crude product (0.9 g) was recrystallised fromCHCl₃-hexane yielding colourless crystals (8a) (0.53 g, 91%). m.p.115-116° C.; R_(f) 0.08 (1:1 hexane-ether v/v). ν_(max) (CHCl₃)/cm⁻¹:3308 (OH), 2967 (CH), 1615, 1552,. 1495 (Ar), 965 (oxadiazole); δ_(H)(250 MHz, CDCl₃) 1.36 (9H, s, (C(CH₃)₃), 2.22 (1H, t, OH), 4.79 (2H, d,CH₂O), 7.53 and 8.06 (8H, m, 2×Ar—H); dc (63.5 MHz, CDCl₃) 21.0 (CH₃CO),31.1 (C(CH₃)₃), 35.1 (C(CH₃)₃), 64.5 (CH₂OH), 121.0 and 123.1 (arylcarbons bonded to oxadiazole ring), 126.1, 126.8, 127.1, 127.3 (Ar)144.7.0 (Ar—CH₂OH), 155.4 (Ar—^(t)Bu), 164.1 and 164.8 (C); [Found: C,74.08; N, 9.03; H, 6.52; C₁₉H₂₀O₂N₂ requires C, 74.0; N, 9.1; H, 6.5%];m/z (EI) 308 (55), 293 (100%), 161 (25) 135 (25), 116 (25) and 77 (25)[Found: (M⁺) 308.1525. C₁₉H₂₀O₂N₂ requires M, 308.1525].

[0068] Preparation of monomer (9a) Triethylamine (1.0 ml, 41.0 mmol) wasadded to a solution or oxadiazole (8a) (0.61 a, 19.8 mmol) in THF (20ml) and stirred under N₂. Methacryloyl chloride (0.9 ml, 84 mmol) wasadded slowly by syringe. The solution was stirred for 2 h at roomtemperature. Cloudiness was observed. Ether (100 ml) was added and themixture was washed with water (100 ml), HCl (2M, 100 ml), and brine (100ml). The combined aqueous washings were then extracted with more ether(100 ml). The combined ether layers were dried over anhydrous sodiumsulfate and the solvent removed under reduced pressure to give anoff-white solid. R_(f)=0.38 (1:1 hexane-ether v/v). After purificationusing flash column chromatography with ether-hexane (1:1 v/v), anddrying, (8a) was obtained as colourless crystals (0.67 g, 91%). m.p.106-109° C.; ν_(max) (CHCl₃)/cm⁻¹: 2966 (C—H), 1720 s (C═O), 1615, 1494(Ar), 965 (oxadiazole); δ_(H) (250 MHz, CDCl₃) 1.36 (9H, s, ^(t)Bu),1.99 (3H, t, J 1.313, CH₃), 5.27 (2H, s, CH₂), 5.63, 6.20 (2H, 2,CH═CH), 7.55 and 8.10 (8H, m, 2×Ar—H); XXXδ_(c) (100 MHz, CDCl₃) 18.3(CH₃), 31.1 (C(CH₃)₃), 35.1 (CMe₃), 65.7 (CH₂—O), 121.0 and 123.8 (Ar),126.1, 126.2, 126.8, 127.1, 128.4, 139.8 and 155.5 (Ar), 164.0 and 164.7(carbons in the heterocycle), and 167.0 (C═O); [Found: C, 73.40; H,6.35; N, 7.50; C₂₃H₂₄O₃N₂ requires C, 73.4, H, 6.4, N 7.4%]. m/z (EI)376 (80), 361 (100%), 161 (40), 69 (40) and 41 (65) [Found: (M⁺)376.1787. C₂₃H₂₄O₃N₂ requires M, 376.17868].

EXAMPLE 2

[0069] The Synthesis of Methacrylate Monomer PBD (9b)

[0070] Synthesis of1-(4-nhenyl-benzoyl)-2-(4-acetyloxyl-methyl-benzoyl)-hydrazine (6b): Thesynthesis is similar to that of (6a) except hydrazide (5b) was usedinstead of hydrazide (5a). After isolating the clay-like solid, it wasrecrystalised in 95% ethanol and dried at 100° C. under vacuum to givewhite crystals (6b) (88%). R_(f) 0.28 (ether); δ_(H) (250 MHz, CDCl₃)2.13 (3H, s, CH₃), 5.15 (2H, s, CH₂), 7.44 (5H, m, Ar—H), 7.65, 7.92(8H, m, Ar—H); δ_(C) (63.5 MHz, CDCl₃) 20.9 (CH₃), 65.4 (CH₂), 127.2,127.8, 128.0, 129.0, 130.0, 131.0 (Ar), 139.8 (Ar-Ph₂), 140.5 (CC═O),145.1 (CCH₂) 164.7 (C═O), 170.7 (C═O). ν_(max) (chloroform)/cm⁻¹: 3407,3234 (N—H), 3013 (C—H), 1736 (CO—O), 1635, 1448 (Ar), 965 (oxadiazole).[Found C, 69.8; H, 5.1; N, 7.0; C₂₅H₂₀N₂O₃ requires C, 71.11; H, 5.19;N, 7.21%].

[0071] Synthesis of2-(biphenyl)-5-(4-acetyloxy-methyl-phenyl)-1,3,4-oxadiazole (7b): Thecyclodehydration of (6b) to form (7b) is similar to the preparation of(7a). Thus, (6b) (11.95 g, 30.76 mmol) was dissolved in POCl₃ (40 ml).After refluxing for 6 h, POCl₃ was removed by distillation beforepouring the residue into ice water to obtain a light grey powder whichwas then washed with water (5×200 ml) until neutral. The crude productwas purified by flash column chromatography using hexane-ether (1:1,v/v). (7b) was obtained as colourless crystals (5.57 g, 40%).m.p.130-132° C.; R_(f) 0.71 (ether); δ_(H) (250 MHz, CDCl₃) 2.16 (3H, s,CH₃), 5.20 (2H, s, CH₂), 7.50, 7.72 and 8.22 (13H, m, Ar—H); δ_(C) (63.5MHz, CDCl₃) 20.9 (CH₃CO), 65.5 (CH₂), 122.6, 123.7 (C-oxadiazole),127.1, 127.3, 127.4, 127.7, 128.2, 128.6, 129.0 (Ar), 139.8, 144.6(C-Ph), 164.3, 164.6 (oxadiazole), 170.7 (C═O); ν_(max)(chloroform)/cm⁻¹: 3013 (C—H), 1737 (CO—O), 1614, 1550, 1484 (Ar), 965(oxadiazole). [Found C, 74.76; H, 4.75; N, 7.54; C₂₃H₁₈N₂O₃ requires C,74.58; H, 4.90; N, 7.56.0%].

[0072] Synthesis of2-biphenyl-5-(4-hydroxyl-methyl-phenyl)-1,3,4-oxadiazole (8b): (7b) (7.0g, 18.9 mmol) and sodium hydroxide (1.33 g, 33.3 mmol) were dissolved inethanol (95%, 350 ml) and stirred at room temperature for 3 h beforepouring the reaction mixture into sodium carbonate solution (600 ml) toobtain a white precipitate. The product was then dissolved in ethylacetate, washed with water (3×300 ml) and dried with anhydrous sodiumsulfate. The solvent was evaporated off and drying in vacuo yielded (8b)as fine white crystals (5.6 g, 90%). m.p.168-171° C.; R, 0.71 (ether);δ_(H) (250 MHz, CDCl₃) 2.25 (1H, br, OH), 4.81 (2H, s, CH₂), 7.48 (5H,m, Ar—H), 7.70 (4H, m, Ar—H) and 8.15 (4H, m, Ar—H); 8c (63.5 MHz,CDCl₃) 64.7 (CH₂), 122.7, 123.1 (C-oxadiazole), 127.2, 127.4, 127.7,128.2, 129.0 (Ar), 139.8, 144.5 and 44.9 (C-Ph, CCH₂), 164.5(oxadiazole); ν_(max) (CCl₃)/cm⁻¹: 3692, 3610 (OH), 3015 (H bonded OH),1614, 1551 1484 (Ar), 965 (oxadazole). [Found: C, 76.87; H, 4.75; N,8.27. C₂₁H₁₄N₂O₂ requires C, 76.81; H, 4.91; N, 8.54%].

[0073] Synthesis of methacrylate PBD monomer (9b): (8b) (3.86 g, 11.76mmol) was dissolved in dry THF (150 ml) and dry triethylamine (12 ml,0.49 mol), and stirred at 0° C. Methacryloyl chloride (3 ml, 0.28 mol)was then added dropwise with a syringe. After stirring for 2 h and then,warming up to room temperature, the cloudy solution was poured into icewater (600 ml) to get a white precipitate which was washed with water(5×150 ml) and then, dried to obtain the monomer (9b). TLC showed mainlyone spot. R_(f) 0.38 (1:1 44ether-hexane v/v). The crude monomer wasthen further purified with flash column chromatography usingether-hexane. (9b) was obtained as white crystals (3.78 g, 81%).m.p.123-125° C. (possible polymerisation). δ_(H) (250 MHz, CDCl₃) 2.01(3H, s, CH₃), 5.29 (2H, S, CH₂), 5.64 (1H, S, CH=C), 6.21 (1H, s, CH═C),7.50 (5H, m, Ar—H), 7.72 (4H, m, Ar—H) and 8.22 (4H, m, Ar—H). δ_(C)(63.5 MHz, CDCl₃) 18.4 (CH₃), 65.7 (CH₂), 122.7, 123.7 (C-oxadiazole),126.2, 136.0 (C═C), 140.0, 144.6, 127.2, 127.4, 127.7, 128.2, 128.4,129.0 (Ar), 164.3 and 164.6 (oxadiazole), 167.1 (C═O); ν_(max)(C-Cl₃)/cm⁻¹: 3012 (C—H), 1717 (CO—O), 1614, 1550, 1483 (Ar), 965oxadiazole). [Found: C, 75.5; H, 4.9; N, 6.9. C₂₅H₂₀N₂O₃ requires C,75.74; H, 5.08; N, 7.07%].

EXAMPLE 3

[0074] The synthesis of methacrylate monomer TPV (16)

[0075] Synthesis of the Alcohol (15)

[0076] To a solution of the bis-phosphonate (11) (3.3 g, 8.73 mmol) inDMF (30 ml), cooled to 0° C., was added sodium hydride (1.0 g, 25.0mmol, 60% dispersion in mineral oil). The reaction mixture was stirredfor 15 minutes. The substituted benzaldehyde (12) (1.75 g, 9.1 mmol) andterepthalaldehyde mono(diethyl) acetal (12) (2 ml, 10.05 mmol) in DMF(10 ml) was then added from a dropping funnel and the reaction mixturewas then stirred for 2 h at 0° C. in a cooling bath. HCl (3M, 10 ml) wasadded drop-by-drop to the cooled reaction mixture in order to destroyexcess NaH and remove the acetal protecting group. The acidified mixturewas stirred for 2 h at room temperature and then poured into a largeexcess of distilled water. The crude mixture of products (yellow solids)were filtered out urner suction and dried in vacuo. TLC(CH₂Cl₂)indicated three different compounds in the mixture of products. Thesecompounds were separated by flash column chromatography (CH₂Cl₂). Thedesired aldehyde (14) was obtained (1.11 g, 32.1%).

[0077] The aldehyde (14) (1.1 g, 2.78 mmol) was dissolved in THF (30 ml)and cooled to 0° C. LIAlH₄ (0.2 g, 5.0 mmol) was added slowly in twoportions. The mixture was then refluxed overnight at 60° C. Dilute acid(1M, 100 ml) was added, drop-by-drop to the cooled reaction mixture, todestroy excess LiAlH₄ and dissolve the alumina sludge formed. Theaqueous mixture was extracted with CH₂Cl₂ (3×50 ml). The three CH₂Cl₂portions were combined, washed with brine (50 ml), dried with anhydroussodium sulfate and CH₂Cl₂ was evaporated off to yield the crude alcohol(15). The product was purified by flash column chromatography (elutingwith 1:1 CH₂Cl₂-hexane to CH₂Cl₂ v/v) and was obtained as ayellowish-green solid (1.01 g, 2.54 mmol, 910%). [Overall yield: 29.1%);R_(f) 0.53 (CH₂Cl₂); ν_(max) (KBr)/cm⁻¹ 3386 (OH), 1493 (C═C), 1456(C═C), 1362 (Ar), 1248 (C—O); δ_(H) (400 Mz, CDCl₃) 1.34 (9H, s, t-Bu),3.87 (3H, s, OCH₃), 4.70 (2H, d, J 4.6, CH₂), 6.84 (1H, d, J 8.5, C═CH),7.05-7.15 (3H, m, J 9.4 and 6.4, C═CH), 7.27 (1H, d, J 2.5, Ar—H), 7.36(2H, d, J 8.1, Ar—H), 7.46-7.55 (7H, m, Ar—H), 7.59 (1H, d, J 2.5, Ar—H)

[0078] Synthesis of Methacrylate Ester (16)

[0079] To a solution of alcohol (15) (1.01 g, 2.54 mmol) andtriethylamine (0.6 ml, 4.3 mmol) in dry CH₂Cl₂ (20 ml), was addedmethacryloyl chloride (0.4 ml, 4.09 mmol). The mixture was stirred atroom temperature for 3 h. TLC(CH₂Cl₂) showed no presence of startingmaterial (15). CH₂Cl₂ (80 ml) was added to the reaction mixture whichwas then washed with Na₂CO₃ (50 ml), HCl (1M, 50 ml) and brine (50 ml).The aqueous portions were extracted with a further portion of CH₂Cl₂ (50ml). The two CH₂Cl₂ portions were combined, dried with anhydrousmagnesium sulfate and CH₂Cl₂ was evaporated off to yield the crude ester(16). The product was purified using flash column chromatography(eluting with 1:6 CH₂Cl₂-hexane followed by 1:4 CH₂Cl₂-hexane v/v). Theester was obtained as a green solid which luminescences blue under uvradiation (0.76 g, 1.63 mmol, 64.2w). R_(f) 0.13 (1:9 ether-hexane v/v);ν_(max) (KBr)/cm⁻¹ 1716 (C═O), 1638 (C═C), 1603 (C═C), 1515 (Ar), 1494(Ar), 1462 (Ar), 1156 (C—O); δ_(H) (400 MHz, CDCl₃) 1.34 (9H, s, t-Bu),1.97 (3H, s, CH₃), 3.88 (3H, s, OCH₃), 5.19 (2H, s, CH₂), 5.59 (1H. 's,C═CH), 6.16 (1H, s, C═CH), 6.84 (1H, d, J 8.6, C═CH), 7.05-7.14 (3H, m,J 11.0 and 5.2, C═CH), 7.28 (1H, d, J 2.4, Ar—H), 7.36 (2H, d, J 8.1,Ar—H), 7.46-7.56 (7H, m, Ar—H), 7.60 (1H, d, J 2.4, Ar—H); δ_(C) (100MHz, CDCl₃) 167.29 (CO₂), 154.94 (C), 143.34 (C), 137.71 (C), 137.44(C), 136.17 (C), 135.34 (C), 128.91 (C), 128.53 (C), 128.40 (C), 127.71(C), 126.89 (C), 126.83 (C), 126.61 (CH), 125.85 (CH), 125.64 (C),124.19 (CH) 123.55 (CH), 110.65 (CH), 66.22 (CO₂CH₂Ar), 55.65 (OCH₃),34.19 (CMe₃), 31.56 (C(CH₃)₃), 18.37 (CH₃)

EXAMPLE 4

[0080] The polymerisation of Methacrylate PPD Monomer by AnionicPolymerisation (PMA-PPD-1)

[0081] Premaration of (2,6-di-tezt-butyl-4-methylphenoxy)diisobutylaluminium [Al(BHT)^(i)Bu₂]: Di-tert-butyl-4-methylphenol(4.412 g, 20.0 mmol) was dissolved in toluene (20 ml). Triisobutylaluminium (20 ml, 1M in toluene) was added by syringe, under N₂. Thetemperature was allowed to rise to 50° C. while butane gas was evolved.The mixture was then stirred at 50° C. for 1 h. The flask was sealedwith a septum and the mixture used as a stock solution.

[0082] The Polymerisation:

[0083] n-Butyl lithium (0.05 ml, 15%) and Al(BHT)Bu₂ (1.5 ml) weredissolved in toluene (2 ml) and stirred under nitrogen for 30 mins at 0°C. A solution of the monomer (14) (0.33 g, 0.9 mmol) in toluene (2 ml)was at first slowly added dropwise and a yellow colour formed. Themonomer was then run in more quickly. After 2 h, the colour haddisappeared and the reaction appeared to have stopped. More BuLi (0.05ml, 15%) was then added. After a further 3 h, no polymer was observed byTLC. The reaction was therefore terminated by adding methanol. CH₂Cl₂(200 ml) and water (100 ml) were added and the polymer was found at thebottom of the flask. The polymer was then extracted with excess CHCl₃.The solvent was removed under reduced pressure and the resulting polymerdissolved in the minimum amount of CHCl₃, filtered through a sand filledpipette and added to MeOH (200 ml). The resulting white polymer wascollected by filtration giving polymer (15) (ca. 50 mg), m.p. 190-230°C.; ν_(max) (KBr)/cm⁻¹ 2961, 1734 s (C═O), 1617, 1495, 1138, 1067 and842; 6H (250 MHz, CDCl₃) 1.24 (12H, bs, α-CH₃ and C(CH₃)₃ group), 1.77(2H, b, CH₂), 5.29 (2H, s, CH₂), 7.37 and 7.88 (2×4H, b, Ar—H); c (63.5MHz, CDCl₃) 31.0 (CH₃ and C(CH₃)₃), 35.0 (C(CH₃)₃) 44. (p₂), 66.1(CH₂—OH), 120.8, 123.8, 125.9, 126.6, 126.9, 129.1, 138.4, 155.2, 163.6and 164.5 (Ar) and 176.5 (C═O). [Found: C, 64.6; H, 5.9; N, 6.3;C₂₃H₂₄O₃N₂ requires: C, 73.4; H, 7.4; N, 7.4%]; GPC assay revealed(CHCl₃, polystyrene as standard): M_(n)=36,000, M_(w)=489,000.

EXAMPLE 5

[0084] Polymerisation of methacrylate PPD monomer (9a) by radicalpolymerisation (PMA-PPD-2): Monomer (9a) (0.33 g, 0.89 mmol) wasdissolved in AIBN solution in benzene (5 ml, 0.3 mg, 1.83×10⁻⁶ mol). Theratio of AIBN/monomer is 0.21% (mol/mol). After removing ca. 4 ml ofbenzene in vacuo, the solution was thoroughly degassed by severalfreeze-thaw-pump cycles (five to eight times). The reaction mixture wasstirred at 80° C. for 2 h before cooling down to room temperature. Theviscous reaction mixture was poured into MeOH (10 ml) to obtain a whiteprecipitate which was then, washed with MeOH (3×2 ml) and dried to yieldcrude polymer (9a) (0.22 g, 69%). The polymer was further purified bydissolving in chloroform and reprecipitation in MeOH (repeated 3 times).δ_(C) (250 MHz, CDCl₃) 0.67, 0.98 (3H, b, α-CH₃), 1.24 (9H, C(CH₃)₃),1.87 (2H, CH₂), 4.87 (2H, b, CH₂), 7.37, 7.88 (2×4H, Ar—H); δ_(C) (100MHz, CDCl₃) 16.9, 19.0 (α-CH₃), 31.0 (C(CH₃)₃), 35.0 (CMe₃), 45.0 (CH₂),54.1 (CC═O), 66.1 (CH₂OCO), 120.8, 123.8, 125.9, 126.7, 126.9, 129.1,138.5, 155.2 (Ar), 163.7, 164.5 (oxadiazole), 176.8 (C═O); ν_(max)(CHCl₃)/cm⁻¹: 2966 (C—H), 1728 (C═O), 1615, 1552, 1494 (Ar), 964(oxadiazole); [Found: C, 72.69; H, 6.30; N, 7.22; C₂₃H₂₄N₂O₃ requires:C, 73.38; H, 6.43; N, 7.44%]; GPC assay revealed (CHCl₃, polystyrene asstandard) M_(n)=52,000, M_(w)=127,000, M_(w)/M_(n)=2.46.

EXAMPLE 6

[0085] The Polymerisation of Mathacrylate PPD Monomer (9a) by RadicalPolymerisation Method (PMA-PPD-3)

[0086] The polymerisation procedure is similar to Example 5 except AIBNwas used as initiator (0.5% by mol with respect to amount of monomer).After purification by dissolving in CHCl₃ followed by precipitation intoMeOH (repeated three times), polymer (9a) was obtained (55-%). GPC assayrevealed (CHCl₃, polystyrene as standard): M_(n)=34,000, M_(w)=103,000,M_(w)/M_(n)=2.99.

EXAMPLE 7

[0087] Polymerisation of Methacrylate PBD (9b) (PMA-PBD-1)

[0088] The polymerisation of monomer (9b) is similar to that of (9a) inExample 5. Thus, monomer (9b) (0.35 g of, 0.885 mmol) was dissolved in abenzene solution containing AIBN (5.4 ml, 0.73 mg AIBN)(AIBN/monomer=0.50, by mol). Excess benzene was evaporated of in vacuountil ca. 0.5 ml to 1.0 ml of benzene remained in the reaction mixture.The solution was then completely degassed using several freeze-thaw-pumpcycles (five to eight times). The reaction mixture was stirred at 80° C.under a N₂ atmosphere, for 2 h. On cooling to room temperature, theviscous reaction mixture was Doured into methanol-acetone (20 ml, 1:1v/v) to obtain a white precipitate. The polymer was then purified byrepeatedly dissolving in CHCl₃ and precipitating into methanol-acetone(repeated 3 times). After drying in vacuo, (9b) was obtained as a whitepowdery solid (0.23 g, 66w). H (250 MHz, in CDCl₃) 0.66-0.98 (3H, b,α-CO₃), 1.90 (2H, b, CH₂), 4.86 (2H, b, CH₂), 7.28, 7.47 (9H, b, Ar—H),7.85 (4H, b, Ar—H); δ_(C) (100 MHz, CDCl₃) 18.5 (CH₃), 29.5 (CH₃), 44.9(CH₂), 65.7 (CH₂), 122.7, 123.7 (Ar-oxadiazole), 126.9, 127.2, 127.4,127.7, 128.1, 128.4, 128.8 and 129.0 (Ar), 139.4, 144.5 (Ar-Ph,Ar—CH₂O), 163.8 (C, oxadiazole), 164.2 (C, oxadiazole); ν_(max)(KBr)/cm⁻¹: 3010 (C—H), 1730 (CO—O), 1614, 1550, 1484 (Ar), 964(oxadiazole); [Found: C, 74.44; H, 4.92; N, 6.66; C₂₅H₂₀N₂O₃ requires:C, 75.74; c, 5.08; N, 7.07%]; GPC assay revealed (CHCl₃, polystyrene asstandard): M_(n)=89,000, M_(w)=103,000.

EXAMPLE 8

[0089] The Polymerisation of Mathacrylate Monomer PBD (9b) (PMA-PBD-2):

[0090] The polymerisation procedure is similar to Example 7 exceptchlorobenzene rather than benzene, was used as solvent. The polymer wasthen purified by repeatedly dissolving in CHCl₃ and precipitating intomethanol-acetone (repeated three times). (9b) was obtained in 50% yield.GPC assay revealed (CHCl₃, polystyrene as standard): M_(n)=4,080,M_(w)=42,500.

EXAMPLE 9

[0091] The Polymerisation of Methacrylate TPV (16) (PMA-TPV):

[0092] The polymerisation of monomer (16) is quite similar to that ofmonomer (9). Thus, monomer (16) (0.205 g, 0.44 mmol) was dissolved inbenzene solution (2.5 ml) containing 0.35 mg of AIBN (10.8 mg, 0.85mmol). The solution was then concentrated by evaporating off somebenzene in vacuo and then thoroughly degassed by using thefreeze-thaw-pump method (repeated five times). The reaction mixture wasthen stirred at 80° C. for 2 h under an inert nitrogen atmosphere. Thehomopolymer was precipitated out in excess methanol and purified bydissolving in CHCl₃ and reprecipitation in excess MeOH (repeated twice).The polymer was dried overnight in vacuo and was obtained as a paleyellow powdery solid (0.11 g, 54%). ν_(max) (KBr)/cm⁻¹ 1720 (C═O), 1613(C═C), 1514 (Ar), 1465 (Ar), 1150 (C—O); OH (400 MHz, CDCl₃) 0.5-1.1 (b,backbone α-Me), 1.1-1.25 (b, backbone CH₂), 1.29 (9H, s, C(CH₃)₃), 3.74(3H, s, OCH₃), 4.6-5.2 (2H, b, CO₂CH₂), 6.7-7.1 (2H, b, CH═CH), 7.1-7.7(13H, b, CH═CH and Ar—H); l_(max)/nm (CHCl₃): 245, 324; GPC assayrevealed (CHCl₃, polystyrene as standard) M_(n)=161,000, M_(w)=702,000,M_(w)/M_(n)=4.37.

EXAMPLE 10

[0093] ‘Screened’ Anionic Polymerisation of Methyl Methacrylate. ofMethacrylate Monomer TPV (16) by Anionic Polymerisation: 10.1Preparation of 2,6-di-tert-butyl-4-methylphenoxy) Diisobutylaluminium[Al(BHT)^(i)Bu₂l

[0094] Di-tert-butyl-4-methylphenol (4.412 g, 20.0 mmol) was dissolvedin toluene (20 ml). Triisobutyl aluminium (20 ml, 1M in toluene) wasadded by syringe, under N₂. The temperature was allowed to rise to 50°C. Butane gas was evolved. The mixture was then stirred at 50° C. for 1h. The flask was sealed with a septum and the mixture was used as astock solution.

[0095] 10.2. Polymerisation of Methyl Methacrylate

[0096] A solution of Al(BHT)^(i)Bu₂ (3 ml, 1.5 mmol, 0.5M in toluene)was mixed with toluene (15 ml) in a 3 neck 100 ml RB flask fitted with apresure equalising dropping funnel, N₂ balloon and a spetum.tert-Butyllithium (0.3 ml, 1.7M in pentane) was then added by syringe,with stirring. Several minutes were allowed to elapse to permit completecomplexation of the two metal alkyls. Methyl methacrylate (MMA) (2 ml,1.87 g, 18.7 mmol) was added drop-by-drop from the dropping funnel. Themixture was stirred at 0° C. for 1 h. The addition of MMA produced apronounced yellow colour in the solution but on completion of thepolymerisation, the solution is colourless. The polymer was precipatedout in excess hexane and dried in vaccuo overnight. Yield (1.7 g, 90%);m.p. 173-2800C; ν_(max) (KBr)/cm⁻¹ (1731 (C═O), 1150 (C—O); δ_(H) (400MH\, CDCl₃) 0.75-1.1 (b, 3H, α-CH₃), 1.7-2.1 (b, 2H, CH₂), 3.59 (s, 3H,CH₃); Tactility δ_(H) (triad, %); 0.83 (rr, 68.8%), 1.01 (mr, 31.2a).GPC in chloroform revealed M_(n) 25,980, M_(w)/M_(n)=1.35.

EXAMPLE 11

[0097] The Copolymerisation of Methacrylate PBD and TPV:

[0098] The copolymerisation of monomer (9b) and monomer (16) was beencarried out using radical copolymerisation method that is similar tohomopolymerisation. Thus, monomer (9b) (0.211 g., 0.532 mmol) and (16)(0.250 g, 0.537 mmol) were first dissolved in a benzene solution (6.5ml) that contain 0.8839 mg of AIBN (AIBN/(17+18)=0.5%, by mol) to form ahomogeneously dispersed solution. The solution was then concentrated toca. 1 ml by evaporating off some benzene in vacuo and then, completelydegassed by using the freeze-thaw-pump method (repeated five times). Thereaction mixture was stirred at 80° C. for 2 h under an inert nitrogenatmosphere. After cooling down to room temperature, the viscous solutionwas poured into MeOH (20 ml) to obtain a white precipitate which wasthen further purified by repeatedly dissolving in chloroform andprecipitating into methanol (repeated three times). The copolymer wasobtained as a light yellow powdery solid (0.29 g, 63%). δ_(H) (250 MHz,CDCl₃) 0.67-1.16 (2×3H, b, 2×a-CH₃), 1.33 (9H, s, ^(t)Bu), 1.61 (4H,CH₂), 3.88 (3H, OCH₃), 4.82 (4H, s, CH₂), 6.72-7.9 (24H, b, Ar—H); δ_(C)(100 MHz, CDCl₃) 31.5 (C(CH₃)₃), 34.1 (CMe₃), 55.5 (OCH₃), 110.5(CH═CH), 123.4, 124.0, 126.6, 127.0, 127.2, 127.4, 127.8, 128.2, 128.5,129.0, 137.4 (Ar); ν_(max) (KBr)/cm⁻¹ 2949 (C—H), 1724 (C═O), 1610, 1548(Ar), 961 (oxadiazole); GPC assay revealed (CHCl₃, polystyrene asstandard) M_(n)=44,000, M_(w)=242,000, M_(w)/M_(n)5.45.

EXAMPLE 12

[0099] Poly(methacrylate) P-D as Single Electron Transporting Layer:

[0100] In order to evaluate the applicability of the polymers in LEDdevices, two double layered LED devices have been fabricated using PPVas a hole transport layer and either aluminium or calcium as thenegative electrode.

[0101] LED device fabrication: ITO glass was cleaned in an ultrasonicbath with detergent solution for 20 minutes and then rinsed withdistilled water, acetone and isopropanol before drying in a stream ofN₂. The dry and absolutely clean ITO glass substrate was thenspin-coated with a PPV precursor solution (1% in methanol) at roomtemperature at 2000 rpm for 20 minutes. Thermal conversion of the PPVprecursor was carried out at 280° C. in vacuo (ca. 0.1 mmHg) for 4 h toobtain a PPV layer (with thickness of ca. 40 nm). The PPV layerfunctions as both a hole-transport and light-emitting layer. Theoxadiazole containing polymer PRA-PPD-2 (usually 2% in chloroform) wasthen spin-coated onto the converted PPV layer before depositingaluminium on the top to form the double layer LED device. The electrodeswere led out using a copper adhesive tape strip and then covered withPVC adhesive tape to prevent contact with air. (1) ITO/PPV/PMA-PPD/Al Nolight emission bellow 28 V (2) ITO/PPV/PMA-PPD/Ca Green yellow lightemission

[0102] The above results show that when aluminium is used as thenegative electrode, incorporation of a PMA-PPD layer in the double layerdevice has no apparent benefits. However, light emission (below 28V) isenhanced when calcium is used as the cathode. FIG. 1 shows that theinternal quantum efficiency of the double layer device (2) can beincreased by about four folds, while the turn-on voltage is apparentlyreduced (FIG. 2).

EXAMPLE 13

[0103] Poly(methacrylate) (PPD) used as an Electron Transporting Layerin the Form or a Blend, with Stilbene Containing Poly(methacrylate)Derivative (TPV):

[0104] Alternatively, PMA-PPD has been used in a blend with a bluelight-emitting polymer (PMA-TPV), with PPV being used as a holetransporting layer, in a series of devices. These devices werefabricated using the similar procedure described in Example 12, exceptPKA-TPV (2% in chloroform), and a blend solution of PMA-TPV andPMA-PPD-2 (1:1 w/w in chloroform) were used instead. (3) ITO/PMA-TPV/CaNo light emission (4) ITO/PPV/PMA-TPV/Ca No light emission (5)ITO/PPV/Blend of PMA-TPV + Blue light emission and gradual PMA-PPD/Cachange to green light emission (6) ITO/PPV/PMA-TPV + No light emissionPMA-PPD/Al

[0105] These results suggest that PMA-TPV does not electroluminesebellow 28V unless an electron transporting polymer PMA-PPD is also used(device 3). For device 4, blue light emission was initially observed butthe colour gradually changed to green within 20 minutes on continuouscharge application at a bias voltage of ca. 15V (as shown in FIG. 3).FIG. 4b shows that the internal quantum efficiency of the deviceincreased after storing the device for a week.

EXAMPLE 14

[0106] Poly(methacrylate) PBD as Single Electron Transport Layer:

[0107] According to the LED fabrication procedure described in Example12, PMA-PBD-1 solution in chloroform was spin-coated onto a PPV layer,on an ITO glass substrate, thus forming a LED device using PMA-PBD asthe electron transporting layer: (7) ITO/PPV/PMA-PBD/Ca. Green lightemission

[0108] Green light emission was observed when a bias voltage of 15V wasapplied.

EXAMPLE 15

[0109] Poly(methacrylate) PBD used as Electron Transport Layer in theForm of a Blend with poly(methacrylate) TPV as the Emitting Polymer:

[0110] A blend solution of PMA-PBD-1/PMA-TPV(1:1 w/w) in chloroform wasused to spin-coat a film onto a layer of PPV, on an ITO glass substrate.(8) ITO/PPV/PMA-PBD + PMA-TPV/Ca Blue light emission

[0111] Blue light emission was observed at a bias voltage of 20V in thefirst 30 minutes followed by a continuous green light emission (FIG. 5).The PMA-PBD polymer is used as an electron-transporting functionallayer, while the PMA-TPV polymer was used to produce blue lightemission. The PMA-TPV polymer also exhibits some cross-linkingpotential.

EXAMPLE 16

[0112] Poly(methacrylate) PBD-TPV Copolymer Used as a Blue LightEmitting Layer, in a Double Layer Device:

[0113] In an series of LED devices, it has been found that incorporationof PMA-PBD showed no benefit in enhancing light-emission from a PPV orPMA-TPV layer, when aluminium was used as the cathode [devices (9) and(10)]. However, PBD segments in the copolymer PMA-TPV-PBD does enhanceor aid blue light emission from the TPV chromophores in the copolymer[asshown in device (13)]. (9) ITO/PPV/Al No light emission (10)ITO/PPV/PMA-PBD/Al No light emission (11) ITO/PPV/PMA-TPV/Al No lightemission (12) ITO/PPV/Blend of PMA-TPV + Blue light emission but lessstable PMA-PBD/Al (13) ITO/PPV/Copolymer of Blue light emissionPMA-TPV-PBD/Al

[0114] These results suggest that the use of electron transportingsegments in the copolymer is better than that in the form of a blend[compare device (12) with (13) and (14)]. FIG. 6 shows that the turn-onvoltage for the device is about 16V, and the light intensity willincrease along with the increase of the applied voltage until 23V(device break-down occurs beyond that voltage)(FIG. 6). It can be seenfrom FIG. 7, that the colour of the light emitted is blue since the peakmaxima in the electroluminescence spectrum is located at 457 nm. This isin the blue region of the visible spectrum. It can also be seen fromFIG. 8 (line 2), that there is light emission from the PPV layer sincethere are two electroluminescent shoulders at 554 nm and 507 nm, whichare typical of PPV emission (FIG. 8 (line 3)]. The PPV emission isfurther confirmed when the colour of light emitted gradually changesfrom blue to green on continuous charge application. This suggest thebreak-down of the TPV chromophores in the PMA-TPV-PBD copolymer, thusleaving PPV as the sole light-emitting polymer. FIG. 9 shows that thedevice has a fairly high internal quantum efficiency (with 0.035%)considering aluminium is used as the cathode.

EXAMPLE 17

[0115] Copolymer PMA-TPV-PBD used as a Blue Light Emitting Layer in aSingle Layer Device:

[0116] The copolymer solution (2% in chloroform) was directlyspin-coated onto a clean ITO glass substrate followed by the depositionof aluminium to form a single layer LED device: (14) ITO/PMA-TPV-PBD/AlBlue light emission

[0117] Blue light emission was observed when a bias voltage (20V) wasapplied but the device appears to be less stable compared to the doublelayered LED device (13).

[0118] The Preparation and Application of Main Chain LED PolymersThrough a Precursor Route

[0119] Poly(methacrylates) have many advantages such as hightransparency, high resistance to chemicals and good mechanical strength.High molecular weight poly(methacrylates) as well as multi-functionalcopolymers can also be easily obtained. However, poly(methacrylate)derivatives may not be good candidates for polymers which exhibit highstability and resistance to an electrical field. Therefore, they mayhave a life-time problem in applications involving LED devices. In orderto prevent this problem, one approach involves the introduction ofanother chain segment which contains cross-linkable groups such as TPV.Another way to improve the resistance to an electrical field is tochoose other types of polymer chains such as rigid-rod polymers orladder polymers. However, there is a severe processability problem forrigid-rod or ladder polymers due to their low solubility in conventionalorganic solvents. The processability of these polymers can be improvedby using a soluble precursor which can be converted to a rigid andconjugated polymer. Here, we have tried a precursor route for thesynthesis of polyaromatic oxadiazoles as shown in Scheme 8 and Scheme 9.

EXAMPLE 18

[0120] Synthesis of Polyaromatic hydrazide (24): 1,3-isophthaloyldichloride (5.31 g, 26.17 mmol) was added to the slurry of (23) (5.08 g,26.17 mmol) in N-methylpyrolidone(NMP) (50 ml) and LiCl (4.86 g) in a250 ml, 3-neck RB flask. The reaction was stirred for 5 h at 0° C.before pouring the viscous reaction mixture into water to obtain a whiteprecipitate which was then washed with 10% LiOH(aq) solution, water andmethanol respectively. The polymer was purified by Soxhlet extractionusing methanol (8 h) and dried in vacuo at 110° C. for 8 h. (24) wasobtained as a white powdery solid (7.82 g, 92%). 6H (200 MHz, DMSO-d,)7.73 (1H, s), 8.15 (2H, d, Ar—H), 8.09 (4H, s), 8.52 (1H, s, Ar—H),10.77 (4H, s, 2×NRNH); δ_(C) (100 MHz, DMSO-d₆) 127.2, 128.5, 130.0,131.4, 133.0, 135.5 (Ar), 165.3 C═O), 165.5 (C═O); ν_(max) (KBr)/cm⁻¹3252 (N—H), 1685 (C═O), 1654 (CO—NH), 1560, 1508, 1488 (Ar); Intrinsicvisicosity: 0.5 dL/g (30° C. in DMSO).

EXAMPLE 19

[0121] Preparation of polyaromatic oxadiazole (25): The polyaromatichydrazide (24) will be thermally converted to (25) at 270° C. (or above)under nitrogen or in vacuo for at least 24 h. ν_(max) (KBr)/cm⁻¹: 1700(residue of CO—NH), 1609, 1543, 1478, 1458 (Ar), 961 (oxadiazole);λ_(max/film): 227, 335 nm.

EXAMPLE 20

[0122] Preparation of polyaromatic hydrazide-tert-Bu (27): A 250 ml3-neck RB flask with a condensor, a mechanic stirrer and thermometer wascharged with (23) (3.88 g, 0.02 mol), 5-tert-butyl-1,3-isodhthalic acid(26) (4.44 g, 0.02 mol), and LiCl (6.0 g) dissolved in dry NMP(60 ml)and dry pyridine (40 ml). The reaction was carried out in the presenceof diphenyl phosphite (14.05 g, 60 mmol) at 120° C. for 2.5 h. Thesticky, opaque solution was poured into methanol (500 ml) to obtain awhite precipitate which was then washed with methanol (4×200 ml) andthen, extracted using methanol in a Soxhlet apparatus for 20 h. Afterdrying in vacuo, (27) was obtained as a white solid (5.85 g, 77%) eH(200 MHz, DMO-d₆) 1.43 (9H, s, C(CH₃)₃), 8.10 (4H, b), 8.20 (2H, b),8.37 (1H, Ar—H), 10.77, 10.80 (4H, 2, 2×NHNH); δ_(C) (100 MHz, DMSO-d₆)31.0 (C(CH₃)₃), 35.1 (CMe₃), 122.1, 124.8, 127.9, 132.9, 135.6, 151.8(Ar), 165.3 (C═O), 165.7 (C═O); ν_(max) (KBr)/cm 3252 (CO—N—H), 2957(C—H), 1654 (CO—NH), 1543, 1478 (Ar); [Found: C, 60.60; H, 5.64; N,14.47. C₂₀H₂₀N₄O₄ requires: C, 63.13; H. 5.30; N, 14.47%].

EXAMPLE 21

[0123] Preparation of polyaromatic oxadiazole-tert-Bu (28): Thepolyaromatic hydrazide-^(t)Bu polymer (27) was thermally converted intopolymer (28) under nitrogen or in vacuo at 270° C. (or above) for atleast 24 h. ν_(max) (KBr)/cm⁻¹ 2957 (C—H), 1543 s, 1482 (Ar), 962(oxadiazole); [Found: C, 68.64; H, 4.65; N, 15.64. C₂₀H₁₆N₄O₂ requires:C, 68.54; H, 4.69; N, 16.28%].

[0124] The Preparation and Application of Main Chain Polymers Throughthe Introduction of Flexible Spacers

[0125] The introduction of a flexible spacer into a conjugated or rigidpolymer chain will usually enhance the solubility of the polymer. Thefollowing examples illustrate the preparation and application of threedifferent polymers with a hexafluopropylene spacer. (Scheme 10)

EXAMPLE 22

[0126] Preparation ofPoly(phenylene-1,3,4-oxadiazole-2,5-diylphenylene-2,2-hexafluoropropylidene)(31): Phosphorus pentoxide (2.95 g, 20.0 mmol) was dissolved inmethanesulfonic acid (20 ml) upon stirring at 80° C. over 30 min.Hydrazine sulfate (1.302 g, 10.0 mmol) and2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (3.923 g, 10.0 mmol) wereadded and the mixture stirred for 24 h at 80° C. The solids dissolvedslowly within 30 min. On cooling to room temperature, the yellow viscoussolution was poured into water (300 ml) and neutralised with saturatedaqueous Na₂CO₃ (40 ml). The precipitate (fibre-like) was filtered outunder suction and washed with water (3×300 ml), and finally purified bydissolving in chloroform and precipitating out in methanol (repeatedthree times). (31) was obtained as grey-white fibres whichmelted/decomposed above 270° C. (2.79 g, 75.4%). λ_(max) (chloroform)300 nm; λ_(max) (solid film) 290 nm; ν_(max) (KBr)/cm⁻¹ 1618, 1585,1551, 1499, 1420, 1256, 1210, 1175, 1140, 1071 10120, 971, 928, 840 723;δ_(H) (400 MHz, CDCl₃) 7.60-8.18 (8H, b, Ar—H); δ_(C) (100 MHz, CDCl₃)122.3, 124.8, 125.3 (ipso-C), 127.1 and 131.0 (CH), 136.5 (ipso-C);[Found: C, 54.99; H. 2.29; N, 7.56. C₁₇H₈F₆N₂O requires: C, 55.15; H.2.18; N. 7.57%]; The polymer was insoluble in ethyl acetate, ether,acetonitrile, toluene and acetone but soluble in tetrahydrofuran,dichloromethane and chloroform. GPC assay revealed (CHCl₃, polystyreneas standard, 10 ml/min flow rate) M_(n)=11,800, M_(w)=143,000,M_(w)/M_(n)=12.

EXAMPLE 23

[0127] The Preparation of Polymer (32):

[0128] The synthesis procedure for polymer (32) is quite similar to thatof polymer (31). Phosphorus pentoxide (2.70 g) was dissolved inmethanesulfonic acid (16.0 ml) upon stirring at 80° C. over 30 min.Hydrazide (23) (1.6355 g, 8.42 mmol) and 2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (3.301 g, 8.42 mmol) were added and the mixturestirred for 24 h at 80° C. After the mixture was cooled to roomtemperature, the yellow viscous solution was poured into water (300 ml)and neutralised with saturated aqueous Na₂CO₃ (40 ml). The precipitatewas filtered out under suction and washed with water (3×300 ml), andfinally purified by Soxhlet extraction with methanol for 48 h. (32) wasobtained as a grey powdery solid which melted/decomposed above 270° C.(3.43 g, 79.2%). λ_(max) (solid film) 312 nm. ν_(max) (KBr)/cm⁻¹ 1725,1617, 1576, 1552, 1497, 1415, 1327, 1256, 1210, 1174, 1140, 1072, 1017s,970, 928, 838, 722; δ_(H) (400 MHz, CDCl₃) 7.43 (4H, s, Ar—H), 7.64 (4H,s, Ar—H), 7.85 (4H, s, Ar-P:); 6c (100. MHz, CDCl₃) 123.8, 124.3 127.2,127.8, 129.8, 130.8, 133.0, 133.8, 141.6.

EXAMPLE 24

[0129] The Preparation of Polymer (33)

[0130] The synthesis procedure or polymer (33) is quite similar to thatof polymer (31). Phosphorus pentoxide (1.860 g) was dissolved inmethanesulfonic acid (12.0 ml) upon stirring at 80° C. over 30 min.Hydrazide (23) (0.611 g, 3.148 mmol), hydrazine sulfate (0.410 g, 3.148mmol) and 2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (2.47 g, 6.30mmol) were added and the mixture stirred for 24 h at 80° C. After themixture had cooled down to room temperature, the yellow viscous solutionwas poured into water (300 ml) and neutralised with saturated aqueousNa₂CO₃ (40 ml). The precipitate was collected by suction filtration andwashed with water (3×300 ml), and finally purified by Soxhlet extractionwith methanol for 48 h. (33) was obtained as a grey powdery solid whichmelted/decomposed above 270° C. (2.54 g, 91.4%). λ_(max) (solid film)320 nm. δ_(H) (250 MHz, CDCl₃) 7.41 (4H, s, Ar—H), 7.90 (4H, s, Ar—H),8.13 (2H, s, Ar—H); δ_(C) (1Q0 MHz, CDCl₃) 124.2, 124.4, 125.0, 127.8,128.5 (C), 130.4, 131.5, 134.5 (CH), 142.3 (C).

EXAMPLE 25

[0131] Polymer (31) as a Single Electron Transport Layer

[0132] Clear polymer (31) solution (1% in chloroform, filtrated through0.45 μl membrane) was spin-coated onto a PPV layer (ca. 40 nm thicknesson an ITO glass substrate). Aluminium was then evaporated on top of thefilm of polymer (31) (ca. 40 nm) to form a double layer polymer LEDdevice (ITO/PPV/P-31/Al]. A more stable green light emission wasobtained at a bias voltage of 22V, in comparision to a device withoutP-31.

EXAMPLE 26

[0133] Polymer (31) as Electron Transporting Polymer in a Blend Formwith Polyalkylthiophene

[0134] A clear blend of polymer solution (1% in chloroform, filtratedthrough 0.45 ul membrane) [1:1 ratio of polymer-(31):poly(3-(2-dimethylethyl) thiophene)] was spin-coated onto a dry and clean ITO glasssubstrate. Aluminium was then evaporated on top of the film of polymerblend (ca. 40 nm) to form a double layer polymer LED device:[ITO/PAT+P-31/Al). A more stable yellow light emission was obtained at abias voltage of 18V, in comparision to a device without P-31.

EXAMPLE 27

[0135] Polymer (32) as Both an Electron Transporting Polymer andElectroluminescent Polymer in a Double Layer Device

[0136] A clear solution of polymer (32) (1% in trifluoroacetic acid,filtered through 0.6 ul pore size membrane) was spin-coated onto a PPVlayer (ca. 40 nm thickness on an ITO glass substrate). Aluminium wasthen evaporated on too of the film of polymer (32) (ca. 40 nm) to form adouble layer polymer LED device: [ITO/PPV/P-32/Al]. Green light emissionwas observed at a bias voltage of 15V, which then turned to blue purplewhen a higher bias voltage (28V) was applied.

[0137] The Synthesis of Polythiophenes 45a-c

[0138] The synthesis of the relevant polythiophenes 45a-c is shown inScheme 11

[0139] The relevant thiophene monomers 1 and 2 have been reported (K. A.Murray, S. C. Moratti, D. R. Baigent, N. C. Greenham, K. Pichler, A. B.Holmes and R. H. Friend, Synth. Met., 1995, 69, 395-396).

[0140] The regioregular polythiophenes chosen to illustratecrosslinkable polymers are poly(3-hexylthiophene)s containing a smallamount of 11-hydroxyundecyl side chains. The monomers have beencopolymerised in ratios of 19:1 1:2 up to 2:1 1:2, to give thetetrahydropyranyl acetal protected copolymers 43. These can bedeprotected to give the alcohol-functionalised copolymers 44 (scheme11). Conversion to the azide is achieved in one step using excessdphenylphosphoryl azide and has been carried out on 19:1, 9:1 and 4:1ratio copolymers 44 to give azidated copolymers 45a, 45b and 45crespectively; no residual alcohol can be seen by ¹H NMR.

[0141] Thermal decomposition of the azide was achieved by heating filmsof polymers 45a-c to 200° C. under vacuum for 30 minutes; differentialscanning calorimetry of polymer 45b indicates that azide decompositionoccurs above 185° C. Azide decomposition results in loss of nitrogen andthe formation of a highly reactive nitrene which is expected to reactfairly indisciminately with single and double bonds. A change in theUV-visible absorption spectra of the polymers is observed oncrosslinking; the spectrum shifts to lower wavelength (higher energy)possibly due to a shorter conjugation length due to nitrene insertionalong the polymer backbone and this effect increases with the azidecontent of the polymer (FIG. 11, Table 1). The resulting films werewashed with chloroform and were insoluble but showed a slight colourchange (Table 1). A small amount of soluble, non-crosslinked polymer waswashed from the 19:1 copolymer (ex 45a) but the remaining polymer wasfully insoluble. TABLE 1 Thermal crosslinking of regioregularpolythiophenes with different azide contents. λ_(max)/nm λ_(max)/nmλ_(max)\nm λ_(max)/nm Ratio before after CHCl₃ in Polymer hexyl:azideheat heat washed chloroform 45a 19:1  520 510 502 458 45b 9:1 522 496488 458 45c 4:1 522 486 482 462

[0142] The resultant insoluble polythiophene films can be used in deviceformation, as further layers might be spun from solution on top of thepolythiophene without causing any damage. It is also possible thatphysical properties could be tailored by altering the azideconcentration and controlling the conjugation length in the polymer.

[0143] Polythiophene Device Embodiment:

[0144] A film of the non-cross linked polythiochene was spun (1000rpm/40 sec) on a ITO coated glass substrate producing a dark red uniformfilm. The substrate is baked at 200° C. for 60 minutes in vacuum (5 10⁻⁶mbar). After cooling the film was carefully washed with chloroform anddried in nitrogen. 1000 A of aluminium is evaporated onto the polymer toform the top contact. Finally the device was encapsulated with anepoxy/glass combination. FIG. 16 shows a typical IV and LI curve. 2cd/sqm emission was observed at about 100 mA/sqcm with 10V drive. Theemission is red and the emission spectrum is shown in FIG. 17.

[0145] In a further embodiment of this invention the UV/VIS propertiesof the crosslinked polymers are retained and show response to thesolvent environment without dissolving significantly. The solid films ofthe crosslinked polymers are all red, but are orange in contact withchloroform or other good solvents (toluene, THF), indicating salvationof the polymers. The absorption spectra for the 9:1 copolymer (45b) areshown (FIG. 11). This property serves the function of allowing thesepolymer films to be used in detection and sensing devices on account oftheir change in optical properties. Changes in chiroptical propertiescould also be detected in crosslinked polythiophenes carrying chirallymodified side chains. In this way, optical devices can be made whichwould function as sensors or chiral thin film affinity surfaces fordetection of various substrates, such as enantiomers, peptides, proteinsand enzymes.

[0146] Crosslinked Cinnamate Ester Derivates

[0147] Poly(methacrylate) polymers 49 (Scheme 12) carrying statisticaloxadiazole side chains, with distyrylbenzene and cinnamate side chainshave been cross linked by photochemical irradiation. The resultingpolymer in a light emitting device emits light blue light efficiently.

[0148] Poly(methacrylates) have many advantages such as hightransparency, high resistance to chemicals, and good mechanicalstrength. It is also relatively easy to synthesise high molecular weightpolymers as well as multi-functional copolymers. A range of aromaticoxadiazole bonded polymers, distyrylbenzene bonded polymers, and thecopolymers bonded with both oxadiazole and distyrylbenzene have beensynthesised and used for electron transporting layer or light emittinglayer. However, the device of these polymers tend not to be very stablewhile working, presumably due to she flexible backbone and easydimerisation between different distyrylbenzene. In order to overcomethis problem, another functional unit that is UV-photosensitivitycrosslinkable, has been copolymerised to achieve polymethacrylate withelectron transporting unit, blue light emitting unit andUV-crosslinkable unit. Better device stability will be expected as theresult of cross linking and therefore suppress polymer chain movementand dimerisation.

[0149] The UV-sensitive 2-(cinnamoyloxy) ethyl methacrylate 47 wassynthesised according to the literature [M. Kato, T. Hirayama, Macromol.Rapid. Commun., 1994, 15, 741). Monomer 47 can be readily polymerised inthe initiating of AIEN. It was found when benzene is used as solvent,large majority of the formed polymer is insoluble in common organicsolvent, indicating the cross link reaction has been simultaneouslyresulted during polymerisation. When the polymerisation is carried outin THF, fully soluble polymer can be obtained at 60° C. for 8 hours. Thesolvent THF obviously not only plays a solubilising role, but alsocontrols the reactivity of radical species.

[0150] The copolymerisation of the aromatic oxadiazole unit 46,distyrylbenzene unit 48 and the monomer 47 was carried out under asimilar conditions for the homopolymer. The ratio among the monomers canbe varied. For convenience, equal weights of the monomers have been usedfor the copolymerisation that corresponds to p=0.53, q=0.28 and r=0.19(Scheme 12). Yellow powdery copolymer 49 can be obtained in good yieldafter purification (precipitate twice in methanol). The copolymer 49 issoluble in chlorinated solvents, THF and toluene but insoluble inhexane, methanol. GPC analysis revealed that the molar mass of 49 is11,200/53,500 (M_(n)/M_(w)). Free standing polymer film can be easilyobtained by casting technique. The polymer has good stability if it iskept in the refrigerator at <0° C.

[0151] The polymer 49 fluoresces greenish blue under UV light.

[0152] The photocrosslinking behaviour of the copolymer 49

[0153] The three unit copolymer contains not only a luminophore and anelectron transporting chromophore, but also a UV-sensitive cross linkingunit. In order to understand the photocrosslinking behaviour of thepolymer, a thin film of the polymer was exposed in UV-light for varioustime. It can be seen from FIG. 14 that the copolymer exhibits 3absorption peaks in the solid state at 200 nm, 295 nm and 400 nm. Withincreasing exposure time, the intensity of these 3 peaks decreased. Thepeaks at 295 nm and 200 nm are related to the cinnamoyloxy group whichwill be decreased as the result of cross linking. The effect on the IRabsorption of the cinnamoyl ester carboxyl group is seen in Table 2.When a film polymer 49 (on a glass plate) was exposed for S minutes, thefilm became insoluble in chloroform but still fluoresced blue.Therefore, 5-10 minutes exposure time was appropriate for obtaining across linked and insoluble polymer. The PL spectrum of the resultingcross-linked polymer film showed little change upon further irradiationand maintained constant luminescence efficiency (39%). TABLE 2 Thechange of ester group infrared absorption with UV exposure time Time/m 01 6 16 26 40 60 80 110 IR 1722 1722 1723 1724 1725 1727 1728 1729 1729peak (cm-1)

[0154] LED Application

[0155] Two LED devices have been fabricated using PPV as holetransporting layer and copolymer 49 with and without UV irradiation (5minutes) as emissive layer:

[0156] A ITO/PPV/Polymer 49/Al: Pale blue emission (20 V/0.8 mA) B)ITO/PPV/Polymer 49 irradiated/Al: Pale blue emission (28 V/0.8 mA)

[0157] The above results show that polymer 49 can be successfully usedas a blue light emitting polymer using stable aluminium as cathode.Moreover, the spin-coated emissive polymer can be easily cured by UVirradiation to become insoluble which leads to crosslinked polymer andresults in a more stable polymer LED.

[0158] A single layer light emitting device using the polymer 49 as anemissive layer and calcium as cathode has also been made. Blue lightemission has been observed with 0.1% internal quantum efficiency. For asingle layer device, the quantum efficiency is relatively high. Theelectroluminescence spectrum of the single layer device using polymer 49is shown in FIG. 15.

[0159] Representative Synthesis of Polymer 45b

[0160] Reaioreaular 9:1Poly{3-hexyl-co-3-(11-[2-tetrahydropyranyloxy])-thi ophene} (43b)

[0161] Following the above procedure (for polymer 43a) a mixture of2-bromo-3-hexylthiophene (41) (1.47 g, 5.95 mmol) and2-bromo-3-(5-(2-tetrahydropyranyloxy]undecyl)-thiophene (42) (0.28 g,0.67 mmol) was polymerised (with one addition of NiCl₂ (dppp) catalyst)to give copolymer 43b (108 mg, 9%) as a deep purple solid film. λ_(max)(CHCl₃/nm) 450; δ_(H) (200 MHz, tDCl₃) 0.91 (t, J 6.4, 6′-H [3H] ofhexyl), 1.20-1.80 (br m, side-chain CH₂), 2.81 (2H, br t, J 7.6, 1′-H),3.31-3.54 (0.2H, m, 11′, 6″-H [2H] of 11-THPO-undecyl), 3.66-3.90 (0.2H,m, 11′, 6″-H [2H] of 11-THPO-undecyl) 4.57 (0.1H, m, 2″-H [1H] of11-THPO-undecyl) and 6.98 (1H, s, 4-H); GPC (CHCl₃, 450 nm)/Da M_(n)9,5000, M_(w) 13,400, polydispersity 1.42.

[0162] Regioregular 9:1 Poly{3-hexyl-co-3-(11-hydroxyundecyl)thiphene}(44b)

[0163] Following the above procedure (for polymer 44a), regioregular 9:1poly{3-hexyl-co-(11-[2-tetrahydropyranyloxylundecyl) thioph ene} (43b)(117 mg) was treated with methanol/dilute aqueous HCl to givedeprotected copolymer 44b (104 mg, 93%) as a deep purple solid film.λ_(max) (solid/nm) 526, 550 sh, 600 sh, (CHCl₃/nm) 450; δ_(H) (200 MHz,CDCl₃) 0.91 (br t, J-6.4, 6′-H (3H] of hexyl), 1.20-1.80 (br m,side-chain CH₂), 2.81 (2H, br t, J-7.5, 1′-H), 3.62 (0.2H, t, J 6.5,11′-H [2H] of 11-hydroxy-undecyl) and 6.98 (1H, s, 4-H); GPC (CHCl₃, 450nm)/Da M_(n) 11,500, M_(w) 17,000, polydispersity 1.65.

[0164] Regioregular 9:1 Poly{3-hexyl-co-3-(11-azidoundecyl)thiophene}(45b)

[0165] Following the above procedure (for polymer 45a), regioregular 9:1poly{3-hexyl-co-3-(11-hydroxyundecyl)thiophene} (44b) (77 mg) wasazidated to give copolymer 45b (63 mg, 81%) as a deep purple solid film.λ_(max) (KBr disc)/cm⁻¹ includes 2095 w (azide); λ_(max) (solid/nm) 522,550 sh, 600 sh, (CHCl₃/nm) 450; δ_(H) (200 MHz, CDCl₃) 0.91 (br t,J-6.7, 6′-H [3H] of hexyl), 1.20-1.80 (br m, side-chain CH₂), 2.81 (2H,br t, J-7.4, 1′-H), 3.23 (0.2H, t, J-7, 11′-H (2H] of 11-azidoundecyl)and 6.98 (1H, s, 4-H); GPC (CHCl₃, 450 nm)/Da M, 5,100, M 11,800,polydispersity 2.34; DSC: exotherm at 185° C., max. at 200° C. (not seenon second sweep—nitrene formation); TGA (%/° C.) 99.5/185, 95.5/270,55/480, <10/600 (N₂ loss=1.6%)

1. A process for the production of a semiconductive polymer, whichprocess comprises providing a luminescent film-forming solventprocessible polymer and cross-linking the solvent processible polymerunder conditions so as to increase its molar mass whereby the polymer ismade resistant to solvent dissolution and retains its semiconductive andluminescent properties.
 2. A process according to claim 1, wherein thestep of cross-linking the solvent processible polymer is effected usinga cross-linking method selected from thermal cross-linking, chemicalcross-linking or photochemical cross-linking.
 3. A process according toclaim 1, wherein the polymer includes a luminescent main chain.
 4. Aprocess according to claim 3, wherein the main chain comprises apolythiophene copolymer capable of luminescence.
 5. A process accordingto claim 4, wherein the polythiophene copolymer is of the generalformula

in which R′ is a solubilising group, R″ is a spacer group cross-linkingthe main chain to another polymer, and x, y and n are each integers,wherein x:y is in the range 19:1 to 1:2 and n is in the range 3 to 100.6. A process according to claim 5, in which R′ is —C₆H₁₃ and R″comprises —(CH₂)₁₁—.
 7. A process according to claim 1, wherein thepolymer includes a luminescent side chain.
 8. A process according toclaim 7, wherein the luminescent side chain is linked to the polymermain chain by a spacer.
 9. A process according to claim 8, wherein theluminescent side chain comprises a distryryl benzene derivative.
 10. Aprocess according to claim 7, wherein the polymer comprises apolymethacrylate.
 11. A process according to claim 1, wherein thepolymer includes a charge transport segment in the polymer main chain orcovalently linked thereto in a charge transport side chain.
 12. Aprocess according to claim 11, wherein the charge transport segmentcomprises a moiety Ar₁-Het-Ar₂ in which Ar₁ and Ar₂ are the same as ordifferent from one another and are each aromatic units; and Het is aheteroaromatic ring, the electronic structure of which favours chargetransport.
 13. A process according to claim 12, wherein the solventprocessible polymer comprises a luminescent polymer of general formula

in which p, q and r are independently each integers in the range 1 to100.
 14. A cross-linked semiconductive polymer capable of luminescencein an optical device, and being resistant to solvent dissolution, whichpolymer is obtainable according to the process of claim
 1. 15. A polymeraccording to claim 14, wherein the cross-linking is formed in a stepselected from thermal cross-linking, chemical cross-linking andphotochemical cross-linking.
 16. A polymer according to claim 14, whichincludes a luminescent main chain.
 17. A polymer according to claim 16,wherein the main chain comprises a polythiophene copolymer capable ofluminescence.
 18. A polymer according to claim 17, wherein thepolythiophene copolymer is of the general formula

in which R′ is a solubilising group, R″ is a spacer group cross-linkingthe main chain to another polymer, and x, y and n are each integers,wherein x:y is in the range 19:1 to 1:2 and n is in the range 3 to 100.19. A polymer according to claim 18, in which R′ is —C₆H₁₃ and R″comprises —(CH₂)₁₁—.
 20. A polymer according to claim 14, which includesluminescent side chain.
 21. A polymer according to claim 20, wherein theluminescent side chain is linked to the polymer main chain by a spacer.22. A polymer according to claim 20, wherein the luminescent side chaincomprises a distryryl benzene derivative.
 23. A polymer according toclaim 20, wherein the polymer comprises a polymethacrylate polymercapable of luminescence.
 24. A polymer according to claim 14, whichincludes a charge transport segment in the polymer main chain orcovalently linked thereto in a charge transport side chain.
 25. Apolymer according to claim 24, wherein the charge transport segmentcomprises the moiety Ar₁-Het-Ar₂ in which Ar₁ and Ar₂ are the same as ordifferent from one another and are each aromatic units; and Het is aheteroaromatic ring, the electronic structure of which favours chargetransport.
 26. A polymer according to claim 25, which comprises aluminescent polymer of general formula

in which p, q and r are independently integers in the range 1 to 100.